The present invention relates to cranks for use in human-powered machines such as bicycles and crank-driven exercise machines and relates particularly to such a crank equipped with a unidirectional clutch and a coupler engageable to prevent the clutch from permitting the crank to rotate in either direction with respect to the shaft.
It is known to connect cranks drivingly to crankshafts through unidirectional clutches in exercise machines and bicycles, as taught in Day U.S. Pat. No. 5,860,329. Use of such clutches is known as a way to assist in training a person's muscles. While pedals equipped with such clutches are useful, use of the clutches is not always desired, as it may be preferred at times to use a crank to move a shaft optionally in either rotational direction, particularly in exercise machines. It may also be desirable to use a unidirectional clutch for specific training purposes during a portion of a bicycle ride, but it also may be desirable to use the same bicycle with its cranks fixed to extend conventionally in opposite directions during a portion of the same bicycle ride. It would also be desirable to use a stationary exercise machine equipped with a crank or a pair of cranks driving an input crankshaft through unidirectional clutches at some times, yet to be able to have cranks fixed in a conventional oppositely-directed arrangement to drive the shaft optionally in either direction at other times, or to permit one crank to move the other one of a pair at times. The cost of two bicycles or two exercise machines equipped with differently connected cranks would usually not be justified, and the time required to exchange cranks equipped with clutches for cranks fixed to a crankshaft so as to rotate the crankshaft positively in either direction is also unacceptable.
What is desired, then, is a crank assembly that can be used to drive a crankshaft in either of two modes. In a first mode, a unidirectional clutch should permit free rotation of the crank in one direction with respect to the crankshaft, but couple the crank to the crankshaft drivingly when the crank is moved in an opposite rotational direction. In a second mode, the crank should be coupled drivingly to the shaft so as to drive the shaft in either direction, and the mechanism should be able to be shifted between the two modes simply and quickly.